Current vs Voltage Characteristics for C-Series Modules with Current Limiting Architectures

Updated Jul 30, 2018

Reported In

Reported In shows products that are verified to work for the solution described in this article. This solution might also apply to other similar products or applications.

Hardware

NI-9421

NI-9422

NI-9423

Driver

NI-DAQmx

Issue Details

What input impedance should I expect when using a C-Series module with a current limiting architecture (9421, 9422 and 9423)?

Solution

National Instruments does not specify an input impedance for such modules because impedance is a strong function of voltage. In general, knowing what current to expect at a given voltage is more useful than knowing the impedance or resistance because the current is relatively constant (by design) in the voltage range this module is normally used in. Below (Figure. 1) is a graph of how current changes with voltage for typical values at 25 Degrees C.